You can make the buttons brighter, but to do so, the screen will get brighter also.
The faceplate has a photo-sensor behind the lens that makes the backlight brighter or dimmer depending on the ambient light.
This setting can be changed so the unit stays bright (or dark).
from an FM screen
press and release the 1,3,and OK buttons at the same time.....this will enter a diagnostic screen.
use the up or down arrows on the faceplate until you get to a screen that reads "Diagnostic Photocell"
It will be set to the default "automatic" setting.
Use the "change" button to switch between "day", "night" and "automatic"
The day setting will increase the intensity of the backlight...but also the screen.
Press "exit" to get back to normal functions
Please try to resist playing with the other settings when in the diagnostic menu.
Bad things can happen.